404 THE SPECIAL SENSES. 



to the several canals. When the horizontal canal is cut on one side 

 in pigeons the animal makes movements of the head in the plane of 

 that canal, and if the similar canal on the other side is also sec- 

 tioned these movements are more pronounced. The animal may 

 also in moving show an inability to walk normally and a tendency, 

 especially when excited, to make abnormal forced movements of 

 rotation of the whole body. After such an operation the pigeon will 

 not fly voluntarily and if thrown into the air is not able to guide 

 its flight with accuracy and soon descends. Similar operations 

 on the anterior or the posterior canals cause movements of the head 

 in the corresponding planes and a tendency in walking or flying 

 to make forced movements — somersaults — forward or backward. 

 When all three canals are cut on one or both sides the animal shows 

 a distressing inability to maintain a normal position. The head is 

 twisted, it is not able to stand unless supported, and any attempt 

 at walking or flying results in violent forced and inco-ordinated 

 movements. The animal makes continual somersaults at each 

 attempt to stand or walk and the head is kept in spasmodic, forceful 

 movements, which may produce injury or death. To preserve the 

 animal from injury after such an extensive operation it is necessary 

 to keep it wrapped in bandages. It should be added that results 

 of this character are obtained only when the membranous canals 

 are injured. If the bony canal alone is cut and even if the peri- 

 lymph is removed by suction no such effects are obtained. At 

 most slight and relatively transient movements of the head are 

 observed. If the exposed membranous canal is pricked with a 

 needle more violent movements result, and if sectioned these move- 

 ments are maintained for a longer period and are accompanied by 

 the other reactions described. Similar effects have been obtained 

 from operations on mammals and other animals, but the results 

 are more pronounced in some animals than in others, varying 

 apparently with the delicacy of the co-ordination necessary to the 

 movements (Ewald). Thus, the movements of walking or flying 

 in the pigeon may be assumed to require a nicer adjustment of the 

 muscles used than is necessary in the swimming movements of the 

 fish, and in correspondence with this idea it is found that opera- 

 tions on the canals of fishes are not followed by conspicuous effects 

 upon the movements of the animals. 



Temporary and Permanent Effects of the Operation. — ^The 

 general effects of operations on the semicircular canals, so far as 

 disturbances of equilibrium and occurrence of forced movements 

 are concerned, resemble those resulting from operations upon the 

 cerebellum, and, as in the case of the last mentioned organ, it is 

 found by most observers that if the animal is properly cared 

 for the severity of the first effects passes off to a greater or less 



